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<div>Hi, </div>
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<div>I've been working on a finite element simulation of a 3 ionic species unsteady electrodiffusion model. The concentrations and the electric potential are defined using a unsteady diffusion equations. All the concentration being coupled to the potential
giving a non symmetrical global system.</div>
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<div>I know that everything works since I've solved the system using LU. So far I've tried a lot of different things, but I am now trying to solve the system using a Schur complement, splitting the system in two groups [concentrations, potential],<span style="font-size: 12pt;"> an</span><span style="font-size: 12pt;">d</span><span style="font-size: 12pt;">
I'm getting slow convergence. Here are the options I'm using. I've also attached a file with the ksp_view and the ksp_monitor.</span></div>
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<div>======<br>
</div>
<div> ksp_type gcr</div>
<div> pc_type fieldsplit</div>
<div> pc_fieldsplit_type schur</div>
<div> mat_type nest</div>
<div> ksp_monitor</div>
<div> ksp_view</div>
<div><br>
</div>
<div>//Options concentrations block</div>
<div><br>
</div>
<div> fieldsplit_a_00_ksp_type gcr</div>
<div> fieldsplit_a_00_pc_type lu</div>
<div> fieldsplit_a_00_ksp_rtol 1.0e-4</div>
<div> fieldsplit_a_00_ksp_atol 1.0e-8</div>
<div><br>
</div>
<div>//Options potential block</div>
<div> fieldsplit_schur_mat_type schurcomplement</div>
<div> fieldsplit_schur_ksp_type gcr</div>
<div> pc_fieldsplit_schur_precondition selfp</div>
<div> pc_fieldsplit_schur_fact_type full</div>
<div> fieldsplit_schur_pc_type lu</div>
<div> fieldsplit_schur_ksp_monitor</div>
<div> fieldsplit_schur_ksp_rtol 1.0e-4</div>
<div> fieldsplit_schur_ksp_atol 1.0e-8</div>
<div><br>
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<div><br>
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<div> ksp_rtol 1.0e-5</div>
<div> ksp_atol 1.0e-5</div>
<div>=====</div>
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<div>First of all, I'm wondering what exactly is showing on the screen when I use the fieldsplit_schur_ksp_monitor? </div>
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<div>Also, why is it printing twice each time as you can see in the attached file? When I use pc_fieldsplit_a_00_monitor (which is not included in the file I sent you because it only does one iteration, as it should since it's solving with LU) it prints it
3 times every time which gets pretty annoying. </div>
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<div>Finally, as you can see, it takes a long time to the fieldsplit_schur_ksp to converge, do you have any idea why it takes over 200 iterations to get down to 1e-02? Is there a way to get it to converge faster?<br>
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<div>Thank you for your time,</div>
<div>Amélie<br>
</div>
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